I had a similar situation with my '90. Replacing the throttle position sensor kept the light off, but I also replaced the temperatur sending unit...the one for the ECU, not the gauge. It sounds more like a faulty sending unit for temperature...a lot less costly: the TPS runs $135.00, (Rock Auto) though they eventually need replacing.
I also replaced the O2 sensor...all of this when I did a minor rebuild.
Not sure if the codes are the same for 94 and 90, but the code also indicates fuel pressure (check the fuel filter). An analog meter is $10 at Mal*Wart, you might as well invest in one so your truck can "speak" to you.
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